Influence of aging temperature on corrosion behavior of Al–Zn–Mg–Sc–Zr alloy

Highlights: • Investigate effect of aging temperature on corrosion behavior of an Al–Zn–Mg–Sc–Zr alloy. • Find the relationship between corrosion and microstructures of the studied alloy. • Corrosion behavior is determined using both electrochemical and immersion tests. • Improvement is due to absence of coarse precipitates and precipitate-free zones. - Abstract: Al–Zn–Mg–Sc–Zr alloy sheets were prepared using water chilling copper mould ingot metallurgy processing which was protected by active flux. The effect of aging temperature on the corrosion characteristics of Al–Zn–Mg–Sc–Zr alloy was investigated by means of exfoliation corrosion testing, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) combined with transmission electron microscopy, scanning electron microscopy and optical microscopy observation. It is found that with increasing the aging temperature the susceptibility to exfoliation corrosion decreases. Electrochemical measurements reveal that at early stage of immersion in testing solution, EIS plots of the samples are composed of a capacitive arc and an inductive loop. Inductive loop disappears with the increasing of immersion time and two time constants in impedance diagrams appear. Moreover, the trends of corrosion resistance are further confirmed by polarization curve and EIS test. In addition, transmission electron microscopy observations show that the improved corrosion resistance from increasing aging temperature is duo to the coarsening of matrix and separated precipitates at the grain boundary, and the increased spacing of grain boundary precipitates